Propeller blade shank



4, 956 G. DAKlN PROPELLER BLADE SHANK Filed July 9, 1954 YHI INVENTOR. Gu A DHK/N HTTORNEY United States Patent Ofiice Patented Aug. 14, 1956 PR'OPELLER BLADE SHANK Guy L. Dakin, Dansville, Mich.

Application July 9, 1954, Serial No. 442,238

8 Claims. (Cl. 170- 159) This invention relates in general to an axial flow propeller and more particularly to a propeller blade having a shank structure which will materially improve the efliciency of the propeller, especially at high tip speeds.

. This application is a continuation-in-part of my application Serial Number 300,546, filed July 23, 1952, now abandoned.

It is well settled that vibration in a propeller blade, which increases with tip speed, reduces the efliciency of the propeller. Present propeller blade constructions have been made about as rigid as possible where a cylindrical blade shank and conventional materials are use Any improvement in present propeller constructions must, therefore, depend largely upon the type of materials used therein, unless the propeller structure itself is modified. Only minor structural changes have been made in recent years and these changes have not been concerned with the blade shank. This lack of interest in the shank is largely due to the fact that said shank has been considered a mere connector between the thrust producing, blade portion of the propeller and the propeller hub.

The blade shank, particularly in fixed pitch propellers, is cylindrical primarily as a matter of convenience. The rotational speed of a large propeller, especially, is limited very materially by its centrifugal force and tip speed. As a result, the blade shank generally rotates at a relatively slow speed. Consequently, moderate alterations in the cross-sectional contour of the shank portion will not materially alfect the propeller thrust and will not materially increase its resistance to rotation.

Having reached these conclusions, and as a result of them, I realized that the blade shank might be advantageously designed to serve some additional function, such as reducing vibrations in said blade by increasing the rigidity thereof. The cylindrical shank construction is best suited to produce strength commensurate with a minimum cross-section to overcome the usual stretching and torsional stresses encountered. However, such construction is but poorly suited to resist vibration. I have been unable to find that any attempt has been made, particularly in metal propellers having a hub and separable blades, to alter the shank structure for additional utilization.

Accordingly, a primary object of this invention is the provision of a propeller having a shank portion which materially increases the rigidity of the entire blade without decreasing the strength or thrust of the propeller or materially increasing the resistance to rotation of the propeller.

A further object of this invention is the provision of a propeller shank, as aforesaid, wherein the cross-sectional area of said shank does not exceed that of a conventional cylindrical shank whereas the strength required to overcome centrifugal force is maintained and the resistance of the shank to vibration and/ or undesired flexion is substantially increased.

Other objects and purposes of this invention will become apparent to persons familiar with this type of equipment upon reading the following specification and examining the accompanying drawings, in which:

Figure 1 is a broken front elevation view of a propeller assembly embodying my invention.

Figure 2 is a side elevation view of said propeller assembly with the hub thereof in central cross-section.

Figure 3 is a sectional view taken along the line IIIIII of Figure 2.

Figure 4 is a sectional view taken along the line IV-IV of Figure 2.

Figure 5 is a sectional view taken along the line VV of Figure 2.

Figure 6 is a sectional view taken along the line VI--VI of Figure 2.

Figure 7 is a sectional view taken along the line VlI-VII of Figure 1.

Figure 8 is a sectional view taken along the line VIII-VIII of Figure 2.

In meeting the objects set forth above, as well as others related thereto, I have provided a propeller blade having a conventional outer thrust or blade portion and an inner shank portion integral with said blade or thrust portion. A connector is secured to the inner end of the shank portion of said propeller blade for connection thereof to the conventional hub mounted upon a propeller shaft. The shank portion of the propeller blade has a core from which three fins extend radially and lengthwise of said core. In the preferred embodiment of the invention, said fins are disposed equidistant from each other about the axis of said core, and the axis of said core is disposed at an angle to the longitudinal axis of the propeller blade.

Construction As shown in Figures 1 and 2, the propeller assembly 10 is comprised of a pair of propeller blades 11 which are substantially identical and both embody my invention. A hub 12 supports said blades 11 in a substantially conventional manner upon the propeller shaft 13. It will be recognized that three or four bladed assemblies are fully contemplated by such disclosure. The hub 12 is secured upon the propeller shaft 13 by means of a lock nut 14 or similar device and covered on its forward face by a spinner 15 in a conventional manner.

Each propeller blade 11 has a blade or thrust portion 16 which may be substantially conventional in shape and cross-sectional contour, as shown in Figures 1, 2, and 3. Secured to the inner end of said thrust portion In is a shank 17 (Figures 1, 2, and 7) which comprises the substance of my invention. 0n the inner end of said shank 17, remote from the thrust portion 16, there may be provided in the case of a separable hub 12, a connector 18. In this particular embodiment, said connector 18 is cylindrical in shape for reception into a similar cylindrical opening in the hub 12 and held therein by the connector pin 19.

The shank 17 has a central, longitudinal core 21 which extends from the thrust portion 16 to the connector 18. Three fins 22, 23 and 24 extend radially from said core 21, as best shown by Figures 4, 5, 6, and 7.

As indicated by the dotted line 25 in Figure 8, and the shifting position of the connector 18 in Figures 3, 4, and 5, the center line 25 of the core 21 is disposed at an angle to the lengthwise axis 20 of the propeller blade 11, which axis is coincident with the axis of the cylindrical connector 18. It will be observed that the inner end of the center line 25 of the core 21 intersects the axis of the propeller blade 11 near the junction of the shank 17 and said connector 18. The outer end of the center line 25 is substantially displaced from the axis of said propeller blade 11 toward the trailing edge .of the blade at the junctionof the shank 17 and thrust portion 16. This particular construction permits the trailing fins 23 and 24 to be reduced in radial extent from the core 21 as said core approaches the thrust portion. 16' so that-they smoothly blend into the contour of said thrustaportionlhzat': about thepoint where Fig.- ure 3 is taken.. This particular point- (Figure 3-); corresponds to the normal. point whereat conventional, cylindrical shank blends. with. the thrust portion; of itsblade. Normally, where: said: cylindnical' shank is used, it is of the same. diameter as the: connecton portion 18. Thus, as shown in Figures 6 and 7, it is apparent that the fins 22,. 23? and 241 may extend; radially substantially beyond the normal diameter of the conventional cylindri cal shank, without any. increase in cross-sectional area. The construction of the two trailing fins 23, 24,. blending' togetherand following, through: into the trailing. edge of the thrust portion 16 of the blade, thus forms a V shaped. stabilising, on bracing element. orstructure built into the back of the blade.

The fin 22. which.blendsinto, and-becomes the leading edge of, the blade or thrust portion-16is=substantially coplanar with said. thrust portion. 161,. as: clearly shown in. Figures 4 and 5. It is; evident. in- Figures 6,- where the centrifugal.forcestinvolved permit, thecross sectional area of the shank: 17 maybe substantially less than the cross sectional area of'the eonnecton 18,- which would normally be the cross sectional! area of.- a conventional cylindrical shank. It will also-be observed that since the leadingedge ofthe: fin 22-. is coextensive with: atleast a. portion of the leading. edge. of the propeller thrust por-- tion 16,, there: is a; substantial streamlining effect produced by my shank structure;

Thus, any disadvantage; in the: fact. that the shank. 17 adjacent the: hub. (Figures 6;. andl 7-): is. substantially wider than the conventional shank: would. be, is adequately compensated for by the cutting efiect produced by the leading fin 22. Furthermore, it will be observed that the trailing fins 23 and-2.4 are. disposed at: an angle to the plane perpendicular tothepath-of rotation, thereby additionally reducing -any disadvantageous effects from the shank design of. thisiinvention. Although the trailing fins 23 and 24 are show-nas being,disposedmpon the core-= 21 approximately 1.80 degrees; from the leading fin 22, such radial placement may be increased or decreased as desired orv required, within-the contemplation-of this invention. It will be observed. that whereas the shank portion of a conventional propeller rotates. at a much lower rotational speed thantthe outer thrustzportion of the blade, the axial movement of: the blade through-the air,

as when mounted. on aircraft: is equal throughout all portions thereof. Accordingly, the flat surface of the leading fin.22 improves ;the braking effects of;the. propeller for conventional. landing purposes without. materially increasing; the resistance-ofthe. entire blade to rotational.

movement on to.- axial; movement whent the bladeisin.

full-feathered position.

Operation While the operation of my invention'is' substantially. evident from the: above: disclosure of. the construction, further details are given relating thereto) Theiprimary function of. my. improved; shank fort atpropeller. blade: isto increase the rigidity of thea'propeller:bladeandlthereby decrease undesirableifiexion and :vibraiiomofithepropeller blade during relatively; high: speed operation; Propeller vibrations; create. turbulence. resulting in" lost efficiency of the; propeller; bladecand excess-.noise: As-shown par ticularly' in Figuresr5 and 6,. anyvforce tendingto-flex thev bladein any'di'rec-tiom is opposed substantially'by' the. lateral extentrofiones orlmore of the fins-22; 23, and 21421 ltpwill, be: observed; that the laterall extent of' each fi'n, including: the core of" the shank, is approximately equal :in 'wid-thntoythe entire diameter'of the conventional cylindrical. shank: represented bythe"connector diameter:

The: rigidity of thiszwebatyperstructure is-well known and- 4 well understood so that further details and reference thereto are not believed necessary.

It will be realized that, although the lengths of the fins 22, 23, and 24 are substantially the same in this particular embodiment, they may be varied with respect to each other. It will be recognized that the exact lengthwise and lateral configurations-of the fins are not necessarily limited to the disclosure provided such structure ultimately blendsinto the thrust portion of the blade 16 at approximately the same pointwhere the normal cylindrical shank would blend into the thrust portion.

As shown' in Figure 8; the inner end of the. center line 25 of the core 21 is substantially coincident with the axis 20 of the entire propeller blade: The amount of this coincidence may be increased materially or decreased until it is little more than an intersection of the two axes, provided there is an angular relation between them.

Although a particular. preferred: embodimentl of my invention has been. described and. disclosed hereim. it: Will' be understood that modifications thereof wbichiliewithin the scope. of such disclosurearefully. contemplated unless specifically stated to the contrary in the: appended claims.

I" claim? 1. A propeller comprising a central rotatable hub: and a plurality of blades extending: radially: outwardly from the hub, each blade including'an outer thrust: p'ortionzand an inner shank portionextendin'gibetween and connecting. the thrust portion and the hub, theshank'. portio'nlofeach' of the blades including. an elongated. core: element and three fins substantially equi-angularly spaced about the core: element and extending: longitudinally of the latter, each; fin,.as=measured in. a.transverse sectionthrough one point of: the. shank portion, having a width greater than its thickness and greater than'the transverse dimension of the core element in-such section, thethree fins being of similar profile and substantially equal thickness in saidsection,.one of theshank-portion fins being co-p'lanar withthe thrusttportionrofi the blade; and the other t'wo fins of the shank. portion progressively decreasingin width from said. one point of the shank portion towardthe thrust portion.

2. A propeller comprising a central rotatablehub and a plurality of blades'extending outwardly from the hubon radial axes, each blade including an outerthrust portion and; extending'between and connectin'g'the thrust portion and the hub, an inner@ shank portion, the shank portion of eachof th'e'blades-including an elongated core" element having an axis disposed-at an-angle'to andintersecting the blade axis, each'blade shank portion=also*in-- cludingthree fins distributed substantially equiangularlyabout the core element, each fin, as measured in=a-trans-- verse section through-the shank, having' a" width greater than-its thickness'andgreater than the transverse'dim'em sionof the'core element in such section.

3; A propeller comprising a central rotatable hub and a pluralityof blades extending radially outwardly from'the hub, each'blade including an outer generally flatthrust portion and an inner shank portion extendingbe= tween and connecting the thrust portion and the-hub, the shank portion of each of the blades including an elongated core element and three fins substantially equiangularly spaced about the core element and" extending longitudi= nallyof" the latter, one'of'thefins of e'achblad'e' being substantially continuous with anddisposed'in the'plane of thethrnstp'ortion, said onefin and the thrust'porti'on of the corresponding blade having side faces merging smoothly'into one another, each fin as measured in a transverse: section through the shank" and at a p'ointof the lattercloser' to thehub thanto the. thrust portion havinga width greater than its thickness and greater than the transverse dimension of the core element in such section, and the fins being of substantially. equal thickness at said section.

4; A propeller comprising a central'rotatable'hub 'and a plurality ofblades extendingradially outwardly fromth'e hub, each blade including an outer thrust portion and an inner shank portion extending between and connectlng the thrust portion and the hub, the shank portion of each of the blades including an elongated core element and three fins substantially equi-angularly spaced about the core element and extending longitudinally of the latter, the widths of the fins of each blade as measured at a point of the shank portion remote from the thrust portion and in a. plane transverse to the axis of the corresponding blade being substantially equal to one another and greater than their respective thicknesses, the width of two of the fins progressively decreasing and the width of the third fin progressively increasing from such point to the thrust portion, and said third fin merging into the outer thrust portion of the blade.

5. A propeller comprising a central rotatable hub and a plurality of similar blades extending outwardly from the hub on radial axes, each blade including an outer thrust portion and, extending between and connecting the thrust portion and the hub, an inner shank portion, the shank portion of each of the blades having a part comprising three equiangularly spaced fins extending longitudinally of the blade and disposed in intersecting relation and a part comprising a connector having a surface of revolution Substantially symmetrical about the blade axis, the hub being formed with radial sockets which receive the connector parts of the blades, the finned part of each blade shank portion also including a central core element extending longitudinally of the blade at the intersection of the fins and of generally less cross sectional area than the connector part, the core element including a tapered base end of progressively increasing cross sectional area toward the connector part, each fin being integral with and extending onto the tapered base end of the core element, and each fin as measured in a transverse section through the shank having a width greater than its thickness and greater than the transverse dimension of the core element in such section.

6. A propeller comprising a central rotatable hub and a plurality of similar blades extending outwardly from the hub on radial axes, each blade including an outer generally flat thrust portion and extending between and connecting the thrust portion and the hub, an inner shank portion, the shank portion of each of the blades having a part comprising three equiangularly spaced fins extending longitudinally of the blade and a part comprising a connector having a surface of revolution substantially symmetrical about the blade axis, the hub being formed with radial sockets which receive the connector parts of the blades, the finned part of each shank portion also including a central core element extending longitudinally of the blade and of generally less cross sectional area than the connector part, the core element being tapered and of progressively increasing cross sectional area toward the connector part, one of the fins of each blade being substantially continuous with and disposed in the plane of the thrust portion, said one fin and the thrust portion of the corresponding blade having side faces merging smoothly into one another, and each fin as measured in a transverse section through one point of the shank having a width greater than its thickness and greater than the transverse dimension of the core element in such section.

7. A propeller comprising a central rotatable hub and a plurality of blades extending outwardly from the hub on radial axes, each blade including an outer generally flat thrust portion and, extending between and connecting the thrust portion and the hub, an inner shank portion, the shank portion of each of the blades including an elongated core element having an axis disposed at an angle to and intersecting the blade axis in the plane of the thrust portion, each blade shank portion also including three fins distributed substantially equiangularly about the core element in intersecting relation, one of the fins of each blade being substantially continuous with and disposed in the plane of the thrust portion, said one fin and the thrust portion of the corresponding blade having side faces merging smoothly into one another, each fin as measured in a transverse section through one point of the shank having a width greater than its thickness and greater than the transverse dimension of the core element in such section, and the fins being of similar profile and substantially equal thickness at said section.

8. A propeller comprising a central rotatable hub and a plurality of blades extending outwardly from the hub on radial axes, each blade including an outer generally flat thrust portion having leading and trailing edges and an inner shank portion extending between and connecting the thrust portion and the hub, the shank portion of each of the blades including an elongated core element having an axis disposed at an angle to and intersecting the blade axis in the plane of the thrust portion, each blade shank portion also including three fins distributed substantially equiangularly about the core element in intersecting relation, one of the fins of each blade being substantially continuous with and disposed in the plane of the thrust portion, said one fin having an edge continuous with the leading edge of the thrust portion of the corresponding blade, the other two fins of such blade forming a V-shaped bracing element merging into the trailing edge of the thrust portion of such blade, each fin as measured in a transverse section through one point of the shank having a width greater than its thickness and greater than the transverse dimension of the core element in such section, and the fins being of similar profile and substantially equal thickness at said section.

References Cited in the file of this patent UNITED STATES PATENTS 1,427,307 Ma Kenny Aug. 29, 1922 1,532,346 Roberts Apr. 7, 1925 2,001,896 Ward May 21, 1935 2,161,932 Peterson June 13, 1939 2,514,487 Griese July 11, 1950 FOREIGN PATENTS 595,288 France Sept. 30, 1925 

